The invention disclosed and claimed herein generally pertains to an improved method for acquiring magnetic resonance (MR) imaging data of a coronary artery, as the artery moves during a cardiac cycle. More particularly, the invention pertains to a method of such type which significantly improves imaging accuracy and efficiency.
As is well known, motion of a coronary artery during a cardiac cycle has two phases or motion components, i.e., motion during systole (mechanical contraction of the heart) and motion during diastole (mechanical relaxation of dilation of the heart). During systole the coronary artery moves from a diastolic position of maximum positional excursion to a systolic position of maximum excursion. During diastole the artery moves from the systolic maximum position back to the diastolic position of maximum excursion.
Because of the continual motion, problems have been encountered in the past, in connection with certain prior art pulse sequences used for MR imaging of coronary arteries. More specifically, when such prior art techniques are employed, the location of the scan plane, that is, the plane in which imaging takes place, may not coincide with the location of the artery. As a result, it becomes necessary to change imaging parameters and acquire further sets of data. Such prior art techniques include acquiring a single image at a single phase of the cardiac cycle; acquiring images at multiple locations, each at a different phase of the cardiac cycle (i.e., single-phase interleaved technique); and acquiring images at a single location but at multiple phases of the cardiac cycle.
For example, in the single image-single phase method, if the timing is off, or if a patient position changes from the time of a preliminary scout scan (used to select the scan plane location) the acquisition will miss the coronary artery. Thus, the scan will have to be repeated, with either a different timing of the scan relative to the cardiac cycle, or at a different scan location.
In regard to the single-phase interleaved method, if the scan locations are incorrectly positioned, or if the scan times are incorrectly estimated, the coronary artery may be missed completely. This is because the pulse sequence used to implement the method acquires an image at different slice locations (in an arrangement using evenly prescribed slice-spacings) and at different times of the cardiac cycle. It is therefore very possible that the coronary artery will not be in the same position or slice location as the excited slice location.
The multi-phase single slice location approach insures that at least one image of the coronary artery will be obtained. However, for tortuous vessels, i.e., those which have a number of kinks or twisted components, or which are otherwise substantially non-coplanar, only a small segment of the coronary artery may be visualized by an image at a sole location. Accordingly, further acquisitions may be needed.
Each of the above techniques requires manual prescription of the scan locations, and relies upon the prerequisite that the vessel is in one of the prescribed scan or slice positions at the appropriate phase of the cardiac cycle. Such techniques may also assume that there is minimal movement during diastole. As descibed above, such methods may miss the coronary artery entirely, or may only capture a segment thereof in one or two images. When this occurs, the scan must be repeated, with a variation of the prescribed slice location, in an effort to visualize a larger vessel segment. Thus, the efficiency of each of the above prior art techniques is comparatively low.